Device for shielding coherent electromagnetic radiation and laser booth provided with such a device

ABSTRACT

The invention relates to a device for shielding coherent electromagnetic radiation, especially laser radiation. The device comprises at least two partially converging faces ( 6, 7 ) between which two opposite openings ( 8, 9 ) are configured. The distance of the faces ( 6, 7 ) between the two openings ( 8, 9 ) varies to such an extent that the electromagnetic radiation is prevented from going from the one opening ( 8 ) straight through the other opening ( 9 ).

The invention relates to a device for shielding coherent electromagneticradiation and to the use of the device of the invention in laser weldingbooths and for shielding coherent electromagnetic radiation in workprocesses.

In the industry, sources of coherent electromagnetic radiation, such aslasers, are increasingly used for machining material, as in welding,soldering and cutting, and in surface treatment. For reasons ofradiation safety, this process takes place in closed or encapsulatedbooths. However, to introduce the workpiece into the booth, transferopenings for robots or transfer devices, such as turntables, are needed.Such transfer openings are closed with rolling or lifting gates, so thatduring the machining of the workpiece, a complete encapsulation of themachining chamber is accomplished. This is necessary so that the MPR(maximum permissible radiation) values outside the machining chamberwill not be exceeded.

In FIG. 1, a laser booth of the prior art is shown. The laser booth 1substantially comprises a plurality of laser-protection walls 2, aturntable 3, and a lifting gate 5. The lifting gate 5 is movable in thedirection of the arrow. The turntable 3, in the exemplary embodimentshown here, is rotatable via a pivot axis 4 such that half of theturntable 3, with a receptacle for a workpiece, is located inside thelaser booth 1 while the other half of the turntable 4, with a secondreceptacle, is located outside the laser booth. Before a workpiece ismachined by the laser in an inner chamber 12 of the laser booth 1, thelifting gate is moved downward, so that a complete encapsulation of theinterior 12 of the laser booth 1 from environment is accomplished. Inthis state, it is not possible for the laser radiation to get out of theinterior 12 into the environment.

While the workpiece is being machined in the inner chamber 12, a furtherworkpiece, which is machined in a subsequent machining step, can beplaced on the second receptacle of the turntable 3. However, before themachined workpiece is rotated out of the inner chamber 12 by means ofthe turntable 3, and the workpiece that has not yet been machined isrotated into the inner chamber 12, the lifting gate 5 must be movedupward again, so that a transfer opening for the workpieces is created.During the time while the lifting gate 5 of the booth is being openedand closed, machining of the workpiece is not possible, which leads tocorrespondingly long cycle times in production.

So-called conical receivers for measuring laser energy are alreadyknown, for instance from Schutz vor optischer Strahluna [Protection fromOptical Radiation] by Dr. Ernst Sutter, VDE-Verlag GmbH, second edition,2002, page 83. In it, hollow-conical absorption faces are used asabsolute receivers or laser beam measurement. The opening angle of thecone is less than 20°, the laser radiation to be measured enters theconical receiver parallel to the cone axis. In its further course, thelaser radiation is reflected toward the tip of the cone. In the case ofradiation entering parallel to the cone axis, the number Z ofreflections occurs before the beam emerges from the cone again, at anopening angle α of the cone of Z=180°/α. It follows that coherentelectromagnetic radiation entering parallel to the cone axis will notreach the tip of the cone but instead, because of the reflections thatoccur, will exit from the cone opening again. Even if the degree ofreflection of the absorption faces of the hollow cone is not very low,still because of the large number of reflections, only a vanishinglysmall fraction of the radiation emerges from the cone again.

Based on this, it is the object of the invention to refine a device ofthe type defined at the outset such that it unnecessary to encapsulatethe chamber in which the radiation source of the coherentelectromagnetic radiation is used.

This object is attained by means of a device for shielding coherentelectromagnetic radiation as defined by the definitive characteristicsof claim 1.

Advantageous features of the invention are defined by the dependentclaims.

According to the invention, two faces converge toward one another, whichbetween them form two diametrically opposed openings; the spacing of thefaces between the two openings varies such that a direct passage of thecoherent electromagnetic radiation from one entrance opening into theother opening is prevented. It is thus attained that practically noradiation from a work chamber to the outside, yet complete encapsulationof the work chamber is not required. Instead, the coherentelectromagnetic radiation is reflected back toward the radiation sourcesfrom the converging faces.

To achieve the highest possible degree of reflection of the two facesconverging toward one another, these faces should form an angle of 10°to 30°, preferably ≦20°, between them.

It is structurally especially favorable if the two faces are embodied asessentially plane, or flat.

In another advantageous feature of the invention, the two faces areembodied as concave and/or convex on their sides facing one another. Asa result of this as well, the direction passage of the coherentelectromagnetic radiation can be prevented without additional shieldingmeans.

It is naturally also conceivable for one face, on its side facing towardthe other face, to be embodied as concave while the other face isembodied as convex.

Another variation is that the two faces extend in concave and/or convexfashion toward one another on their sides converging toward one another.

A reflection of the incident coherent electromagnetic radiation in thedirection of the radiation source can also be achieved if the two faces,on their sides toward one another, have portions that extend in concaveand/or convex fashion.

In another advantageous feature of the invention, at least one baffle isdisposed on at least one face. As a result, by structurally simplemeans, redundance is created, so that in every case, a direct passage ofthe coherent electromagnetic radiation from the inlet opening throughthe other opening is prevented.

To keep the reverse radiation of the coherent electromagnetic radiationin the direction of the radiation source as slight as possible, thefaces and/or the at least one baffle have a surface or a surface coatingof a material that absorbs the electromagnetic radiation. This assuresthat the intensity of the radiation decreases upon each reflection fromone of the surfaces. Even if unwanted scattering of the coherentelectromagnetic radiation occurs between the two faces, this provisionof the invention reduces radiation that might emerge into theenvironment to an amount that is harmless to organic tissue.

It is naturally also conceivable for the faces and/or the at least onebaffle to have a metallized surface or a metallized surface coating,which likewise enhances the degree of reflection of the coherentelectromagnetic radiation, entering between the coherent electromagneticradiation in the direction of the radiation source between the facesconverging toward one another.

In another particular concept of the invention, the device of theinvention for shielding coherent electromagnetic radiation is used inwork processes in which complete encapsulation is either impossible ortoo time-consuming. In particular, it is provided that the device of theinvention be used for shielding laser radiation in a laser booth.

The laser booth may be provided with laser-protection walls, aturntable, with at least one and preferably two recesses for fixing theworkpiece. According to the invention, a laser-protection wall that canrotate with the turntable is located on the turntable, and shieldingdevices are disposed on its peripheral regions.

The shielding devices of the invention may be provided at all the gapsthat occur between the turntable, or the laser-protection wall rotatingwith it, and the adjoining wall of the laser booth. It is understood,however, also to be possible, depending on the operating range of thelaser employed, to provide for instance only one lateral shieldingdevice or two lateral shielding devices and/or only one upper or onlyone lower shielding element, or one upper and one lower shieldingelement. At at least one lateral and/or at least one horizontallyextending peripheral region of the laser-protection wall rotating withthe turntable, there is a face which, with the adjacent laser-protectionwalls themselves or with a fixed face located on them forms convergingfaces. Overall, the result is reflection of the electromagneticradiation into the inner chamber of the laser booth.

Further objects, advantages, characteristics, and possible uses of thepresent invention will become apparent from the ensuing description ofan exemplary embodiment in conjunction with the drawings. All thecharacteristics described and/or shown in the drawing, either alone orin arbitrary appropriate combination, form the subject of the presentinvention, regardless of how the invention is summarized in the claimsand regardless of the claims dependency.

Shown are:

FIG. 1, a laser welding booth in the prior art;

FIG. 2, a laser welding booth with devices according to the invention,located laterally on a turntable, for shielding coherent electromagneticradiation;

FIG. 2 a, the laser booth of FIG. 2, in which devices for shieldingcoherent electromagnetic radiation are provided at the horizontallyextending gaps;

FIG. 3, an enlarged illustration of the device of the invention of FIG.2, in a plan view;

FIG. 4, a device according to the invention of FIGS. 2, 2 a and 3, withan additional baffle; and

FIGS. 5 through 8, further embodiments of the device of the invention.

FIG. 2 shows a laser booth 1, with a device which causes a reflection ofthe otherwise exiting laser radiation back into the booth interior 12.

On a turntable 3 for receiving workpieces, a laser-protection wall 20 isfixedly disposed and is rotatable with the turntable 3 about the pivotaxis 4. To prevent any laser radiation from being able to escape to theoutside through the openings or gaps that result between thelaser-protection wall 20, located on the turntable 3, and the adjacentouter laser-protection walls 2, a wall with a face 6 is disposed on thelaser-protection wall 20. This face 6, as FIG. 3 shows, converges towarda second face 7, which is disposed on the outer laser-protection wall 2.By means of the two faces 6, 7, two openings 8 and 9 are defined, andreference numeral 8 indicates the laser radiation arriving from thebooth interior 12.

The curvatures of the faces 6 and 7 are dimensioned such that upon arotation of the turntable 3 about the pivot axis 4, the face 7, or thewall corresponding to it, is located outside the radius of collisionwith the turntable 3.

Because of the convex embodiment of both the face 6 and the face 7 ontheir sides facing toward one another, it is attained that coherentelectromagnetic radiation cannot escape to the outside from the innerchamber 12 of the laser booth. Instead, the radiation is reflectedmultiple times at the faces 6 or 7, until a back reflection of theradiation into the inner chamber 12 occurs. The radii of curvature ofthe interacting faces 6, 7 are selected such that an angle of ≦20° isformed between their tangents.

Advantageously, devices for shielding the laser radiation are providedat all of the gaps that result between the turntable 3, or thelaser-protection wall 20 rotating jointly with the turntable 3, and theadjoining walls 2 of the laser booth 1. For the sake of greater clarity,in FIG. 2, only the faces 6 laterally disposed on the jointly rotatinglaser-protection wall 20 and the faces 7 corresponding with them on thevertical walls 2 of the laser booth 1 are shown. In FIG. 2 a, thedisposition of the face 6 on the upper, horizontally extendingperipheral region of the jointly rotating laser-protection wall 20, theassociated face 7 on the upper boundary of the opening in the laserbooth 1, and the face 6 on the lower boundary of the opening in thebooth wall 2 are shown; the associated face 7 is formed by the wall ofthe turntable 3 itself.

The faces 6 and 7 have a surface or a surface coating that comprises anelectromagnetic radiation-absorbing material. It is naturally alsoconceivable for the faces to have a mirrored surface. Because of thehigh degree of absorption of the faces 6 and 7, the radiation, aftermultiple reflections, is in every case attenuated such that theintensity of the radiation no longer suffices to harm organic tissue.

To further increase the degree of absorption of the electromagneticradiation between the faces 7 and 6 and thus the intensity of thecoherent electromagnetic radiation, it is possible, as shown in FIG. 4,for baffles 10 to be provided in addition. The entry angle for thecoherent electromagnetic radiation before striking one of the faces 6 or7 is selected to be so large that it is no longer possible, because ofthe multiple reflections and the resultant back reflection, for thecoherent electromagnetic radiation entering through the opening 8 toreach the vicinity of the opening 9. Because of the high degree ofabsorption of the surfaces of the faces 6 and 7 and optionally also ofthe baffle 10, the intensity of the radiation reflected back into theinner chamber is furthermore very slight.

FIGS. 5 through 8 show further exemplary embodiments of the inventionwith different designs of converging faces 6 and 7. The faces 6, 7 inFIG. 5 converge in convex-convex fashion while in FIG. 6 they convergein concave-concave fashion. FIG. 7 conversely shows faces 6 and 7 thatcontain both concave and convex elements. Two respective baffles 10 and11 are shown, which prevent a direct passage of the coherentelectromagnetic radiation through the openings 8 and 9.

In FIG. 8, the converging faces 6, 7, or corresponding wall elements,are embodied as essentially flat, which represents a major structuraladvantage over the other embodiments.

It is furthermore conceivable for the device of the invention forshielding coherent electromagnetic radiation to be used in all workprocesses in which a complete encapsulation is not possible, or foreconomic reasons is too time-consuming. For instance, the device of theinvention can also be used in doors, where once again the exit ofcoherent electromagnetic radiation from an inner chamber that has aradiation source must be prevented.

List of Reference Numerals

-   1 Laser protection booth-   2 Laser-protection wall-   3 Turntable-   4 Pivot axis-   5 Lifting gate-   6 Face-   7 Face-   8 Opening-   9 Opening-   10 Baffle-   11 Baffle-   12 Inner chamber-   20 Laser-protection wall

1-15. (canceled)
 16. A device for shielding coherent electromagneticradiation, having two curved and spaced-apart faces (6, 7), which formtwo essentially diametrically opposed openings (8, 9), characterized inthat the curvatures of the two faces (8, 9) are embodied such that theirspacing varies and a direct passage of the electromagnetic radiationfrom the first opening (8) into the second opening (9) is prevented. 17.The device in accordance with claim 16, characterized in that thesurface, toward the second face (7), of the first face (6) is embodiedas convex, and the surface, toward the first face (6), of the face (7)is embodied as concave.
 18. The device in accordance with claim 1,characterized in that at least one baffle (10, 11) located on one of thefaces (6, 7) is provided.
 19. The device in accordance with claim 18,characterized in that the surfaces, toward one another, of the two faces(6, 7) are embodied as concave.
 20. The device in accordance with claim18, characterized in that the surfaces, toward one another, of the twofaces (6, 7) are embodied as convex.
 21. The device in accordance withclaim 16, characterized in that the surfaces, toward one another, of thetwo faces (6, 7) have concave and convex elements.
 22. The device inaccordance with claim 16, characterized in that the faces (6, 7) have asurface of electromagnetic radiation-absorbing material.
 23. The devicein accordance with claim 18, characterized in that the at least onebaffle (10, 11) has a surface of electromagnetic radiation-absorbingmaterial.
 24. The device in accordance with claim 18, characterized inthat the faces (6, 7) and/or the at least one baffle (10, 11) have ametallized surface or surface coating.
 25. A laser booth having a deviceas defined by claim
 16. 26. The laser booth in accordance with claim 25having external laser-protection walls (2) and a turntable (3), havingat least two recesses for fixing the workpiece, characterized in thatlocated on the turntable (3) is a laser-protection wall (20) that isrotatable with it, on whose peripheral regions faces (6) are located,which form converging faces (7) having the adjacent laser-protectionwalls upon the machining of the workpiece or are located thereon. 27.The use of a device as defined by claim 18 for shielding coherentelectromagnetic radiation in work processes in which a completeencapsulation is not possible or is too time-consuming.